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Gelada Baboons Are Sly Adulterers

Swinging from branch to branch, sifting through the dense, lush foliage of the Amazonian rainforest, a young, subordinate male capuchin monkey stumbles upon a veritable gold mine. It's a cache of figs, all looking tantalizingly sweet and succulent. He picks one and takes a big bite. Delicious.

Other members of the male's troop are nearby, and would undoubtedly want to be notified of the lavish finding. Knowing this, the young male sits back and lets loose a string of loud calls.

But he doesn't emit the softer squeals that would intimate that food is nearby. Instead, he produces a cacophony of barks, hiccups, and coughs, informing the others that a predator is in the vicinity. "Stay away! Danger!" he yells.

Except there is no predator nearby, and no danger, whatsoever. There are only the cherished figs. Instead of apprising the troop of the food's whereabouts, so that they may share in the tasty, nutritious bounty, the subordinate capuchin is deceiving them, so that he can selfishly scoff the figs all by himself!

Deception is a hallmark of the animal kingdom. In the game of life, subterfuge is often synonymous with survival. Most of this trickery occurs between species -- think of all the animals that adopt camouflage to fool predators. However, very little deceit actually occurs within species, where, for the most part, honesty prevails. The capuchin example is a noted deviation, albeit an infrequent one. Human interactions, where dishonesty is quite commonplace, tender a wider selection of examples

But now, researchers have discerned another example of within-species deception, this one among the gelada baboons of the Ethiopian Highlands.

Reporting in the journal Nature Communications, an international team of researchers describes a scandalous subject: how primate adulterers conceal their infidelity.

640px-Gelada_group.jpgCompetition for mating rights is stiff and brutal among gelada baboons. Males of this primate species achieve reproductive success by battling to become the dominant leader of a reproductive unit, which is composed of between one and a dozen females. This means that subordinate males are pretty much out-of-luck. Unless, of course, they can find a female willing to engage in a little lovemaking on the side.

Spending over 2600 hours watching nineteen different baboon reproductive groups, the research team found that such extra-pair copulations are rare, making up only 9% of all copulations. The other 91% were between the dominant male and the females in his unit.

You can probably guess why infidelity is so uncommon. When caught, the act often elicits violent punishment against the cheating pair, courtesy of the dominant male.

Potentially out of the desire to avoid this reprisal, cheating pairs were witnessed to employ two deceptive tactics to conceal their infidelity. First, the baboons were found to significantly suppress their copulation vocalizations. In less scientific terms, they "kept the volume down" while having sex.

Second, the research team found that extra-pair copulations were far more common when the dominant male was greater than twenty meters away. Thus, it seems that the cheaters took into account the visual perspective of the dominant male and decided to mate when his "back was turned," so to speak.

The research team's soap opera-esque findings beg some intriguing questions. Are the baboons' behaviors indicative of higher order cognitive skills? Are they merely a result of more simplistic associative learning? Will the gelada baboons get their own reality television show?

Source: Aliza le Roux, Noah Snyder-Mackler, Eila K. Roberts, Jacinta C. Beehner & Thore J. Bergman (2013) Evidence for tactical concealment in a wild primate. Nature Communications 4:1462 DOI: 10.1038/ncomms2468

(Image: Baboon Unit by Dave Watts via Wikimedia Commons)